When it gets really cold (0 deg F to 5 deg F or so), crystal shapes start to grow overnight. In the morning, they decorate icy stream surfaces, snow at the edge of the stream, and sometimes twigs and branches. I see frost like this near streams most often, but sometimes it grows in hollows and wetlands where there is moisture in the air. When the sun comes out, they vanish.
The title is frost flowers, but they look more like ferns to me.